Refractory gold ores or concentrates are ores which cannot directly be leached with NaCN and contain gold-bearing compounds consisting of arsenopyrites or pyrites comprising more or less organic carbon. They have a relatively low gold content.
Before such ores are leached with cyanide, the sulfur and carbon contents must be oxidized as completely as possible. That oxidation is usually effected by a roasting with oxygen-containing gases. In numerous refractory gold ores the existing contents of arsenopyrite, pyrite and organic compound are not sufficient for the generation of the required reaction heat so that fuel must be added. A large number of refractory gold ores must be roasted at a relatively low temperature to ensure that the subsequent leaching will result in a high yield of gold.
It is known from EP-A-508,542 to roast gold ores at temperatures from 475.degree. to 660.degree. C. and particularly from 500.degree. to 575.degree. C. Coal, butane or propane have been mentioned as fuels to be added. The flash point should be equal to or lower than that of propane. But only an unsatisfactory proportion of propane and butane is combusted to form CO.sub.2 and H.sub.2 O. Coal, if it is used, must be disintegrated to a size which is sufficiently small for use in the fluidized bed.